a)Explain why NH 4 + /NH 3 is areasonable system to use in preparing 2.0L of pH

Question

a)Explain why NH4+/NH3 is areasonable system to use in preparing 2.0L of pH 10.0 buffer. b) And calclate the concentration ratio[NH3]/[NH4] needed to prepare thisbuffer. c) In this particular case, the sum of [NH3] and[NH4] must be 0.5 M. Calculate the[NH3] and [NH4] needed for this buffer. a)Explain why NH4+/NH3 is areasonable system to use in preparing 2.0L of pH 10.0 buffer. b) And calclate the concentration ratio[NH3]/[NH4] needed to prepare thisbuffer. c) In this particular case, the sum of [NH3] and[NH4] must be 0.5 M. Calculate the[NH3] and [NH4] needed for this buffer. b) And calclate the concentration ratio[NH3]/[NH4] needed to prepare thisbuffer. c) In this particular case, the sum of [NH3] and[NH4] must be 0.5 M. Calculate the[NH3] and [NH4] needed for this buffer.

Explanation / Answer

We Know that :      Ammonia is a Weak base so itcan form the basic buffer so in order to form the buffer with pHrange of 10.       According to Henderson'sEquation :         pH = pKa + log [ salt ] / [ Acid ]          10 = 9.25 + log [ NH4+] / [ NH3 ]           [NH4+ ] / [ NH3]   = 5.6234    (b)           TheRatio of [ NH4+ ] / [NH3 ] should be 5.6234 in order to obtainthe pH of 10. The Ratio of NH3 / NH4+            should be 0.1778     (c)           Whenthe sum of concentrations of [ NH3 ] + [ NH4+ ] = 0.5           pH = pKa + log [NH4+ ] / [ NH3 ]            10 = 9.25 + log [ X ] / 0.5 - X             [ X ] / [ 0.5 - X ] = 5.6234              6.6234 X =   2.8117                     X =   0.4245 M          [NH4+ ] = 0.4245 M  ;   [ NH3 ] = 0.0754 M            should be 0.1778     (c)           Whenthe sum of concentrations of [ NH3 ] + [ NH4+ ] = 0.5           pH = pKa + log [NH4+ ] / [ NH3 ]            10 = 9.25 + log [ X ] / 0.5 - X             [ X ] / [ 0.5 - X ] = 5.6234              6.6234 X =   2.8117                     X =   0.4245 M          [NH4+ ] = 0.4245 M  ;   [ NH3 ] = 0.0754 M

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